public static void printAllSub(char[] str,int i,String res) {
		if(i==str.length) {
			System.out.println(res);
			return;
		}
		printAllSub(str, i+1, res);//忽略当前字符
		printAllSub(str, i+1, res+String.valueOf(str[i]));//打印当前字符
	}
	public static void main(String[] args) {
		String aString="abc";
		printAllSub(aString.toCharArray(),0,"");
	}